Safety mechanisms for power tools

ABSTRACT

Various safety systems for power tools, and in particular table saws, include detection systems for detecting a dangerous condition relative to a blade of the power tool, and reaction systems for taking mitigation action in response to detection of a dangerous condition. The safety system may detect, prevent, and/or mitigate a dangerous condition associated with the power tool.

PRIORITY CLAIMS

The present application claims priority to U.S. provisional patentapplication Ser. No. 61/116,098, filed Nov. 19, 2008, entitled “SafetyMechanisms for Power Tools,” which is incorporated herein by referencein its entirety.

BACKGROUND

Many types of power tools have exposed blades, such as table saws andother cutting tools. Contact between the blade and an object other thanthe workpiece can be dangerous. Safety systems to mitigate potentiallydangerous conditions are continually being developed.

SUMMARY

Various new and improved safety systems for power tools, such as tablesaws, are disclosed herein. The disclosed safety systems includedetection systems for detecting a dangerous condition relative to ablade of the power tool, reaction systems for taking mitigating actionin response to detection of a dangerous condition, systems for detectingwhether the blade is spinning, systems for detecting kickback of theworkpiece, and others. Generally, the embodiments described herein maydetect, prevent, and/or mitigate a dangerous condition associated withthe power tool.

In one general aspect, embodiments of the present invention are directedto a table saw that comprises a cutting surface and a motor-driven,rotatable blade for cutting a workpiece on the cutting surface. In oneembodiment, the table saw comprises a kickback detection system fordetecting kickback of the workpiece during cutting of the workpiece. Inaddition, the table saw comprises reaction means in communication withthe kickback detection system for taking a mitigating reaction inresponse to detection of kickback of the workpiece during cutting of theworkpiece by the kickback detection system. According to variousimplementations, the kickback detection system comprises an acousticsensor and a processor in communication with the acoustic sensor. Theprocessor is programmed to recognize a condition indicative of kickbackof the workpiece during cutting of the workpiece based on input from theacoustic sensor. In another implementation, the kickback detectionsystem comprises a torque sensor mounted on the rotatable blade shaftand a processor in communication with the torque sensor, where theprocessor is programmed to recognize a condition indicative of kickbackof the workpiece during cutting of the workpiece based on input from thetorque sensor.

In another general aspect of the present invention, the table sawcomprises a blade-spin detection system for detecting whether the bladeis rotating based on energy from the blade. The blade-spin detectionsystem may be in communication with the reaction means and may providean output to arm the reaction means when the blade-spin detection systemdetects that the blade is spinning. According to variousimplementations, the blade-spin detection system comprises a staticelectricity charge sensor in proximity to the blade for sensing thestatic electricity build-up on the blade. In another implementation, theblade-spin detection system comprises: (i) a transmitter proximate tothe blade for transmitting radio signals; (ii) a passive electroniccircuit on the blade that transmits responsive radio signals whenpassively energized by the radio signals transmitted by the transmitter;and (iii) a receiver, proximate to the blade, for detecting theresponsive radio signals from the passive electronic circuit on theblade. In another implementation, the blade-spin detection systemcomprises an acoustic sensor and a processor, where the processor isprogrammed to determine whether the blade is rotating based on inputfrom the acoustic sensor.

In another general aspect of the present invention, the table sawcomprises a sensor connected to the cutting surface for sensing acharacteristic of the workpiece during, prior to, and/or after cuttingof the workpiece. In various implementations, the sensor comprises aheight sensor for sensing a height of the workpiece relative to thecutting surface. In such an embodiment, the table saw further comprisesa height adjustment circuit that receives an input signal from theheight sensor indicative of the height of the workpiece relative to thecutting surface and outputs a signal to a blade height adjustmentmechanism to adjust the height of the blade based on the height of theworkpiece as sensed by the height sensor. In another embodiment, thesensor comprises a workpiece conductivity sensor on the cutting surfacethat detects electrical conductivity of the workpiece. In such anembodiment, the table saw further comprises contact detection means fordetecting contact with the blade by an object other than the workpiece.The contact detection means receives an input from the workpiececonductivity sensor, which input is used to determine when to triggerthe mitigating reaction means.

In another general aspect of the present invention, the blade comprisesa first electrically conductive blade portion, a second electricallyconductive blade portion, and a dielectric between the first and secondelectrically conductive blade portions. In such an embodiment, the tablesaw may comprise a contact detection system for detecting contact withthe blade by an object other than the workpiece. The contact detectionsystem may be connected to the first electrically conductive bladeportion and drive the first electrically conductive blade portion withan electrical drive signal. The processor of the contact detectionsystem may detect contact with the blade by a foreign object based on anelectrical signal from either the first or second blade portions. Forexample, the processor may detect contact with the blade by a foreignobject based on an electrical signal from the first electricallyconductive blade portion.

In yet another general aspect of the present invention, the table sawcomprises a reaction system for taking a mitigating reaction in responseto detection of a dangerous condition relative to the blade whendetected by the detection system. In various embodiments, the reactionsystem comprises a magnetorheological rotary brake connected to theblade shaft that brakes the shaft to thereby brake the blade in responseto detection of the dangerous condition by the detection system.

These and other advantageous safety systems for power cutting tools willbe apparent from the description below.

FIGURES

Various embodiments of the present invention are described herein by wayof example in conjunction with FIGS. 1 to 54.

DESCRIPTION

The embodiments of the present invention relate generally to safetysystems for power tools having an exposed, moving cutting instrument orblade, such as a table saw. Before describing the various new safetyfeatures, an example table saw is described. FIG. 1 shows one type ofexemplary table saw 10. It includes a table (or tabletop) 12 throughwhich a circular blade 14 extends from beneath the table. The table 12includes a throat plate 13, which includes an elongated slot throughwhich a portion of the circular blade 14 extends. A workpiece (notshown) may be placed on the cutting surface of the tabletop 12 and becut by the portion of the blade 14 extending above the cutting surface.The table 12 and blade 14 are supported by a housing 16 and legs 18. Thehousing 16 may enclose the mechanics that support, position, and drivethe blade 16. The housing 16 may also comprise processor-based systemsfor detecting a dangerous condition relative to the blade, as describedbelow, and/or processor-based systems for detecting the condition of theblade (e.g., whether it is spinning). A motor to drive the blade can bepositioned in or outside of the housing. A switch 20 may be used to turnthe saw on and off, causing blade 14 to spin when turned on. A handle 22may be used to adjust manually the position of the blade 14 relative tothe table 12. For example, using the handle 22, an operator of the saw10 may adjust how far the blade 14 extends above the table 12 or how theblade 14 tilts relative to the top (or cutting surface) of the table 12.A user places a workpiece on the table 12 and slides it into the blade14 to cut the workpiece. Of course, table saws take many differentconfigurations, from large saws sized for industrial use to small sawsthat can be placed on a bench top or counter, and table saws come withvarious types of tables and housings. The safety and other mechanismdescribed below may be employed in most any type of table saw, as willbe apparent from the description below.

FIG. 2 is a diagram showing certain features of a table saw 10 accordingto various embodiments of the present invention. FIG. 2 shows that thetable saw 10 may comprise a detection system 30 that may be used todetect a potentially dangerous condition with respect to the blade 14.In the illustrated embodiment, the detection system 30 may be aprocessor-based capacitive contact sensing system that detects contactof a foreign object with the blade 14 based on a change in an electricalsignal on the blade 14 due to the change in capacitance when the foreignobject contacts the blade 14. The processor of the detection system 30may be, for example, a digital signal processor, a microprocessor, amicrocontroller, or some other type of processor. In such an embodiment,the detection system 30 operates by driving an excitation voltage ontothe blade 14 and detecting the current drawn from the blade 14. Thiscurrent and/or excitation voltage may show changes in amplitude andphase when the blade 14 comes into contact with an electricallyconductive foreign object (such as an operator's hand or finger, as wellas work pieces). The characteristics of these changes can be used totrigger selectively the operation of a reaction system 32, which takesone or more actions to mitigate the detected dangerous condition. Theexcitation voltage may be driven onto the blade 14 via an excitationplate 34, which is capacitively coupled to the blade 14. In such anembodiment, a shield 37 may guard the blade 14 from outside electricalinterference, including the tabletop 12.

More details regarding such capacitive contact sensing detection systems30 may be found in U.S. patent application Ser. No. 11,481/549, entitled“Capacitive sensing system for power cutting tool,” filed Jul. 6, 2006,and U.S. patent application Ser. No. 12/244,994 entitled “DETECTIONSYSTEM FOR POWER TOOL,” filed Oct. 3, 2008, both of which areincorporated herein in their entirety. In other embodiments, thedetection system 30 may comprise two electrodes capacitively coupled tothe blade 14. In such embodiments, the drive signal may be copied to oneof the electrodes. Contact by an object with the blade may be detectedby analyzing the signal from one or both of the electrodes. Thedetection system 30 may also be a proximity sensing system that detectswhen a foreign object comes near (or proximate) to the exposed blade 14.Examples of proximity sensing systems are disclosed in U.S. Pat. No.7,421,932, issued Sep. 9, 2008, and U.S. patent application Ser. No.11/444,712, both of which are incorporated herein by reference in theirentirety. Other types of detection systems may also be used, and thisapplication discloses other types of detection systems.

The blade 14 may be mounted to an arbor or rotatable blade shaft 38. Amotor 40 may drive the arbor 38 to spin the blade 14. The motor 40 maydrive the arbor 38 via one or more belts or gears, or it may use adirect drive.

The blade 14 may be directly driven by the motor or indirectly driventhrough the use of one or more drive belts or gears. The saw 10 may alsocomprise (under the table 12) a bevel adjustment mechanism (not shown)to adjust the angular orientation of the blade 14 relative to the tabletop 12 by pivoting the saw blade 14 and motor. The saw 10 may alsocomprise a height adjustment mechanism (not shown) to adjust the cuttingdepth of the saw blade 14 by vertical movement of the saw blade 14 andmotor. Example embodiments of the bevel adjustment mechanism and theheight adjustment mechanism are provided in U.S. Pat. No. 6,595,096,which is incorporated herein by reference in its entirety.

The reaction system 32 may serve to mitigate the potentially dangerouscondition detected by the detection system 30 by, for example, brakingthe blade 14, dropping the blade 14 below the tabletop 12, or any othersuitable reaction, several of which are described in more detail below.One example reaction system 32 may use an explosive charge to drive astopper (or brake) (not shown) into the blade 14, arresting its motion.In addition, or instead, an example reaction system 32 may drop orcollapse a blade support member (not shown) causing the blade 14 to fallbelow the surface of the table 12. An example blade-drop reaction systemis described in U.S. patent application Ser. No. 11/374,319, filed 13Mar. 2006, which is incorporated herein by reference in its entirety.

In a table saw having a reaction system 32, it is often important tokeep the reaction system 32 operative when the motor 40 powering theblade 14 is turned off, but the blade 14 is still spinning. This isbecause the spinning blade 14, even though the motor is turned off,still represents a potentially dangerous condition. In one embodiment,as shown in FIG. 3, the table saw 10 may comprise an acoustic sensingsystem 300, comprising an acoustic sensor 301, such as a microphone, anda processor 302 (e.g., a DSP or microprocessor). The output of theacoustic sensor 301 may be connected to the processor 302, which maycharacterize the audible and inaudible acoustic energy picked up by theacoustic sensor 301 to detect various operating conditions of the tablesaw. For example, the acoustic sensor 301 could be positioned near, butspaced from, the blade 14, preferably under the tabletop 12 as shown inFIG. 3, to detect whether the blade 14 is spinning. The acoustic sensingsystem 300 may be in communication with the reaction system 32. Inoperation, the processor 302 may compare the acoustic waveforms detectedby the sensor 301 to a database of signature waveforms indicative ofvarious conditions of the table saw 10 in order to detect various statesor conditions of the table saw, such as whether the blade 14 is spinningor not. If, for example, the acoustic sensing system 300 determines thatthe blade 14 is still spinning based on the comparison of the signalsfrom the acoustic sensor of the database of signature waveforms, theacoustic sensing system 300 may signal the reaction system 32 to remainpowered on and operative (e.g., armed). On the other hand, if theacoustic sensing system 300 detects that the blade 14 is spinningslowly, slowing down, or no longer spinning, or if it detects that theblade 14 is about to come to a complete stop, the acoustic sensingsystem 300 may signal the reaction system 32 to disarm.

The acoustic sensing system 300 also may be used to detect otherconditions, such as potentially dangerous conditions. If the acousticsensing system 300 detects such a dangerous condition, the acousticsensing system 300 may send a signal to the reaction system 32 to causethe reaction system to take its mitigating action. Again, the processor302 may compare the input waveforms from the acoustic sensor 301 to adatabase of signature waveforms to detect a dangerous condition. Forexample, the acoustic sensing system 300 may be programmed to detectkickback conditions involving the workpiece being cut by the blade 14.If it detects a kickback condition, the acoustic sensing system 300 mayoutput a signal to the reaction system 32 that triggers the mitigatingreaction of the reaction system 32. The acoustic sensing system 300,based on the output from the sensor 301, could also be programmed todetect various other conditions, such as: (i) motor on with no load;(ii) cutting various types of material (e.g., wood, metal, plastic); and(iii) motor off. The detection of these various states could be used tocontrol different systems of the table saw 10. For example, if theacoustic sensing system 300 detects that the motor is off and the bladeis not spinning, the acoustic sensing system 300 may disarm the reactionsystem 32 so that, for example, maintenance of the table saw 10 may beperformed without activating the reaction system 32. Of course, invarious embodiments, the acoustic sensing system 300 may comprise anumber of acoustic sensors 301 that supply input to the processor 302.The data base of the signature waveforms (for blade spin and/or kickbackor the other conditions) may be stored in a memory unit that is incommunication with the processor 302. The memory unit may be, forexample, a read-only memory (ROM). In various embodiments the ROM may beintegrated with the processor 302.

In another embodiment, as shown in FIG. 4, the table saw 10 may comprisea blade-generated airflow sensing system 400 to detect whether the blade14 is spinning or not. The blade-generated airflow sensing system 400,as shown in FIG. 4, may comprise one or more sensors 401 and a processor402 in communication with the sensors 401. The sensor 401 may includeone or more airflow detection sensors, such as, for example, pressuresensors or hot wire anemometers, that detect airflow generated by theblade 14. To enhance the airflow from the blade 14, the blade 14 maycomprise a number of off-center holes therethrough (i.e., holes that arenot in the center of the blade and that are not used for the bladeshaft). The sensors 401 may detect the airflow generated by the bladeteeth and/or the holes in the blade. The processor 402 may be programmedto detect conditions based on the output signals from the sensors 401,such as whether the blade 14 is spinning or not. If the blade 14 isspinning, the blade-generated airflow sensing system 400 may signal thereaction system 32 to remain armed. If the blade-generated airflowsensing system 400 determines that the blade 14 is not spinning, it maysignal the reaction system 32 to disarm. Again, the processor 302 maydetect whether the blade is spinning by comparing the signals from theairflow sensors 401 to a database of signature waveforms that areindicative of whether the blade is spinning or not.

In another embodiment, one or more vibration sensors (e.g.,accelerometers) may be used to detect whether the blade is spinning.Such vibration sensor may be mounted to the saw 10 in a positionrelative to the blade so that they vibrate in a detectable manner whenthe blade spins.

In another embodiment, as shown in FIGS. 5A-B, one or more magnets 502may be embedded in or placed on the exterior of the blade 14. Inaddition, an inductor 504 may be positioned near the blade 14, such asin the tabletop 12 or under the tabletop 12. As the blade 14 spins, thespinning magnets 502 will induce a voltage across the inductor 504. Thelevel of the voltage across the inductor 504 may be used to controlwhether the reaction system 32 is armed or not. For example, theinductor voltage may be coupled to a control circuit 505 (analog ordigital) that controls whether the reaction system 32 is armed based onthe inductor voltage. If the inductor voltage level exceeds a thresholdlevel, the reaction system 32 may be armed. If the inductor voltagelevel does not exceed the threshold level, the reaction system 32 may bedisarmed.

In another embodiment, the inductor voltage may directly power thedetection system 30 and/or the reaction system 32 with a power converter(not shown) that converts the inductor voltage to input voltage for thedetection system 30 and/or the reaction system 32. That way, thedetection system 30 and/or the reaction system 32 are only powered on solong as the blade 14 is spinning. In such embodiments, the detectionsystem 30 and/or the reaction system 32 may comprise their own,respective, energy storage device to maintain sufficient continuouspower levels.

In another embodiment, as shown in FIG. 6, an electric generator 602 maybe positioned under the tabletop 12 and mechanically powered by thespinning blade 14. The generator 602 may convert this mechanical energyto electricity, which may be used to power the detection system 30and/or reaction system 32. As shown in the embodiment of FIG. 6, thearbor 38 may include a gear 604, which is geared into a gear 606 for thegenerator 602. As shown in FIG. 6, there may be one or more intermediarygears 608 between the arbor 38 and the generator 602. When the arborrotates the armature of the generator 602 is rotated (via the gears604-608) to thereby generate electricity. The electricity generated bythe generator 602 may be used to electrically power the detection system30 and/or the reaction system 32. By using such a generator 602, thedetection system 30 and/or reaction system 32 would be powered when theblade 14 is spinning. That way, the detection system 30 and/or reactionsystem 32 could be powered independently of the motor 40 used to spinthe blade 14. As such, the detection system 30 and/or reaction system 32could be powered even when the motor 40 used to rotate the blade 14 isturned off, as long as the blade/arbor is spinning. This would keep thedetection system 30 and/or reaction system 32 enabled even when thepower to the blade 14 is turned off. Also, the detection system 30and/or reaction system 32 would not be enabled when maintenance is beingperformed on the saw 10 and/or blade 14, as the blade/arbor would not bespinning in such a mode. In other embodiments, the generator 602 may notbe geared to the arbor, but may use a drive belt or some other drivemechanism to drive the generator 602 when the arbor rotates.

In another embodiment, as shown in FIG. 7, the static electricity thataccumulates on the blade 14 may be used to detect a spinning conditionfor the blade 14. The static electricity build-up on the blade may alsobe used to detect contact between the blade 14 and foreign objects. Asshown in the embodiment of FIG. 7, a static charge detection circuit 702may be coupled to, and receive as an input a signal from, the excitationplate 34 that is capacitively coupled to the blade 14. As the blade 14spins, static charge is generated and accumulated on the blade 14. Thestatic charge detection circuit 702 may monitor the static charge on theblade 14, via the excitation plate 34, to detect various conditionspertaining to the blade 14. For example, as the blade 14 slows down, thestatic charge decreases. The static charge detection circuit 702 mayinterpret the decrease in the static charge as an indication that theblade 14 is slowing down. Similarly, by monitoring the static charge onthe blade 14, the static charge detection circuit 702 can detect whenthe blade 14 stops spinning. The detection system 30 and/or reactionsystem 32 may be enabled (e.g., powered on) based on the determinationby the static charge detection circuit 702 of whether the blade 14 isstill spinning. For example, the static charge detection circuit 702 maybe in communication with a controller circuit (not shown) that outputscontrol signals to arm or disarm the detection and/or reaction systemsbased on the output from the static charge detection circuit 702regarding the static charge build-up on the blade 14. In addition, ascontact between the blade 14 and foreign objects (such as the materialto be cut by the blade) will affect the static charge on the blade 14,the static charge detection circuit 702 can be used to detect contactbetween the blade 14 and a foreign object. The detection system 30 mayuse this information from the static charge detection circuit 702 todetermine whether there exists a dangerous condition that warrantstriggering of the reaction system 32. The static charge detectioncircuit 702 may be implemented with analog circuitry, and may alsoinclude digital circuitry in various implementations.

In another embodiment, as shown in FIGS. 8A-B, the blade 14 may compriseone or more embedded passive electronic components or circuits 801. Thepassive circuit components 801 may be embedded in or positioned on oneor both of the sides of the blade 14. In one embodiment, the electroniccomponent 801 may be powered passively by incoming radio frequencysignals from a transmitter 803 near the blade 14, such as embedded inthe tabletop 12, under the tabletop 12, etc. The emitted signals fromthe transmitter 803 may be at a relatively low power so that the passivecircuit components 801 are only passively powered when the circuits 801rotate past the transmitter 803. In one embodiment, the electroniccomponent 801 may comprise a burst RF circuit that, when energizedpassively, emits a burst RF signal to a receiver 805, that may, like thetransmitter 803, be near the blade 14. The output signal from thecircuit component 801 may indicate that the RF circuit 801 is “on” dueto the fact that the RF circuit is powered due to the fact that theblade 14 is spinning. Based on the signal received from the RF circuit801, the receiver 805 may output a signal to the detection system 30and/or the reaction system 32 to remain enabled. In addition, thereceiver 805 may be able to determine the speed of the rotating blade 14based on the number of burst signals received per time period (e.g.,minute or second). That way, the receiver 805 can detect whether theblade 14 is speeding up or slowing down. In other embodiments, thecircuit 801 may comprise a passively powered accelerometer or othermotion sensor, with a transmitter (e.g., an RF transmitter) fortransmitting sensor data to the receiver 805. That way, based on thesensor data, the receiver 805 may determine whether the blade 14 isspinning or not.

In another embodiment, as shown in FIG. 9, the saw 10 may include avariable speed motor 901 for powering the blade 14. In such anembodiment, when the detection system 30 detects a condition thatapproaches the threshold level that triggers the reaction system 32, thedetection system 30 may output a signal to the variable speed motor 901to reduce the speed of the motor 901, to thereby reduce the rate atwhich the blade 14 is spinning. That way, the motor speed may be at areduced level if and when the reaction system 32 is triggered. In suchan embodiment, therefore, the detection system 30 may have at least twotrigger levels: a first trigger level that causes the motor speed of thevariable speed motor 901 to reduce and a second trigger level thattriggers the reaction system 32. The second trigger may be dropping orbraking the blade 14, or some other mitigating reaction as describedherein. Some time after the condition returns below the first triggerlevel, the motor 901 may be returned to full speed. The detection system30 may be a proximity-based or contact-based detection system. Anadvantage of using a variable speed motor 901 is that the speed of themotor may provide feedback to the user regarding potentially dangerousconditions. For example, the reduction in motor speed may provide theuser with advanced warning of a dangerous condition, and the user couldreact to the advanced warning, to thereby potentially avoid themitigating reaction of the reaction system 32.

In another embodiment, as shown in FIGS. 10 a and 10 b, when a dangerouscondition is detected, the detection system 30 may output a signal tochange, or reverse, the direction of the motor 40. Such a mitigatingreaction to a detected dangerous condition may be combined with otherreaction systems 32, such as a braking reaction system (see, e.g. U.S.Pat. No. 6,920,814, which is incorporated herein by reference in itsentirety), a drop mechanism (see, e.g., U.S. patent application Ser. No.11/589,344, which is incorporated herein in its entirety), or othertypes of reaction systems, such as described herein. In particular, fora drop reaction system, the change in angular momentum of the blade 14due to the change in motor direction could be leveraged to increase therate at which the blade 14 drops beneath the tabletop 12.

As another type of reaction system, as shown in FIG. 11, the saw 10 maycomprise a counter-rotating flywheel 1101, which may rotate in adirection opposite the rotational direction of the blade 14. When thedangerous condition is detected by the detection system 30, the reactionsystem 32 may cause a clutch 1103 to engage the flywheel 1101 with thedrive for the blade 14. Preferably, the flywheel 1101 has a mass andspeed such that the angular momentum of the flywheel is equal to theangular momentum of the blade 14. That way, the stored energy of theflywheel 1101 may stop the blade 14 from spinning when the clutch 1103is engaged. If the angular momentum of the flywheel 1101 is greater thanthe angular momentum of the blade 14, the blade 14 may reverse directionwhen the clutch 1103 is engaged. In such an embodiment, a blade-brakingsystem may be used to stop the blade 14 from reverse spinning. If theangular momentum of the flywheel 1101 is less than the angular momentumof the blade 14, the blade 14 may slow down when the clutch 1103 isengaged. Similarly, a blade-braking system may be used in such anembodiment to completely stop the blade 14 from spinning. In oneembodiment, the motor 40 may power both the blade 14 and the flywheel1101, with a transmission being used to provide the reverse rotationaldirection for the flywheel 1101. In another embodiment, a second motormay be used to power the flywheel 1101. The flywheel 1101 may be locatedbelow the tabletop 12.

In another embodiment, the blade 14 may be made out of less massivematerials and/or the blade 14 may have a geometry that lessens the massof the blade 14 (while still providing sufficient structural strength).Using a less massive blade reduces the stored energy in the blade whenspinning, thus allowing the lightweight blade to be stopped or brakedfaster in response to the detection of a dangerous condition. FIG. 12shows three such exemplary blades 14 a-c. In the first embodiment, theblade 14 a comprises an interior portion 1201 and a peripheral portion1202. The interior portion 1201 may be made from a material that is lessdense than the peripheral portion 1202, yet still sufficiently strongand durable. For example, the interior portion 1201 may compriselightweight, strong metals, such as magnesium or titanium, or compositematerials. Suitable composite materials include, but are not limited to,fiber reinforced polymers, carbon-fiber reinforced plastic, glassreinforced plastic, metal matrix composites, ceramic matrix composites,organic matrix/ceramic aggregate composites, thermoplastic compositematerials, or any other suitable composite material. In addition, otherlightweight, strong materials could be used. The peripheral portion 1202of the blade 14 may comprise, for example, conventional blade materials,such as steel, and the material of the peripheral portion 1202 may bemore dense than the interior portion 1201.

In other embodiments, the blade may comprise one or more off-centerholes or openings, as shown in blades 14 b-c, to reduce the mass of theblade. The holes/openings 1207 shown in the example blades 14 b-c areoff-center in the sense that they are not the blade center-hole throughwhich the blade 14 is mounted to its rotatable shaft. In addition, theteeth of the blades 14 b-c could comprise less massive materials, suchas carbide, titanium, aluminum, composite plastics, etc. Blades of thetype shown in FIG. 12 may be used in saws having an airflow-basedblade-spin detection system 400 (See FIG. 4).

In embodiments using a low mass blade, such as described above, the lowmass blade may be coupled to a high-mass flywheel 1301, as shown in FIG.13. The high-mass flywheel 1301 may provide added momentum to the blade14 to aid in cutting workpieces. When a dangerous condition is detected,the reaction system 32 may disengage a clutch that couples the flywheel1301 to the blade drive. That way, the reaction system 32 can moreeasily stop, drop, or otherwise react the lightweight blade, and nothave to additionally stop the high-mass flywheel 1301.

In another embodiment, as shown in FIG. 14, once a dangerous conditionis detected, the reaction system 32 may cause a throat plate 1401,positioned around the blade 14 on the tabletop 12, to pop up. In such anembodiment, the throat plate 1401 may be caused to pop up by a number ofsuitable actuators under the throat plate 1401 that are actuated whenthe dangerous condition is detected, such as for example: pyrotechnicactuators; springs; solenoids; hydraulic actuators; pneumatic actuators;etc. By popping up, the throat plate 1401 may create a guard around theblade 14 and/or knock foreign objects out of the vicinity of the blade14. The throat plate 1401 may be made from a thin piece of metal (e.g.,steel or aluminum), wood, or plastic, for example. As such, it may takeless energy to cause the throat plate 1401 to pop up than it might taketo employ other types of reaction systems. In addition, the pop-upthroat plate 1401 could be combined with other reaction systems, such asbraking reaction systems or blade-drop reaction systems. In addition,according to various embodiments, one side of the throat plate 1401,such as the side at the back of the blade 14, may be pivotably connectedto the tabletop 12. In such an embodiment, when the dangerous conditionis detected, the other end (e.g., the front end or a side) of the throatplate 1401 may be popped up by the actuators causing the throat plate1401 to rotate into the blade 14 and jam the blade 14, potentiallymaking it stop spinning.

In another embodiment, as shown in FIG. 15, when a dangerous conditionis detected by the detection system 30, the tabletop 12 may pop up.Preferably, the tabletop 12 may be lifted or popped up to an elevationlevel that is the same as, close to, or greater than the elevation levelof the top of the blade 14. That way, the tabletop 12 can remove objectsfrom around the vicinity of the exposed blade 14. In one embodiment, thetabletop 12 may be actuated, for example, by pyrotechnic charges inresponse to detection of the dangerous condition by the detection system30, although other suitable actuation means may be used, such aspneumatic actuators, hydraulic actuators, magnetic actuators (e.g.,solenoids), etc. Preferably, the tabletop 12 is moveably connected tothe remainder of the base 16 of the table saw 10 by connectors 1501 thatprevent the tabletop 12 from coming loose from the base 16 when thetabletop is elevated in response to detection of a dangerous condition.

The number of actuators will depend on, among other things, the forcesupplied by each actuator, their placement, and the mass/size of thetabletop 12. In one embodiment, actuators are placed in each corner ofthe tabletop 12, near the connectors 1501. In other embodiments, theactuators are located in two corners of the tabletop 12, so that thetabletop 12 effectively hinges upward when the dangerous condition isdetected. The pop-up tabletop 12 could be combined with other reactionsystems, such as a dropping blade. Also, the pop-up tabletop 12preferably is combined with a guard system that prevents the workpiecefrom flying away when the tabletop 12 pops up.

In another embodiment, the reaction system 32 may cause the geometry ofthe blade 14 to change in response to detection of a dangerous conditionby the detection system 30. As shown in the example of FIG. 16, theblade 14 may comprise an elongate, moveable member 1601 between eachtooth 1603 of the blade 14. The members 1601 may be connected at a pivotpoint 1604 to the blade 14, such that the members 1601 have one free endand one fixed, or pivoting, end. In normal operating conditions, themoveable member may be in the normal or stored position, as shown bymoveable member 1601 a in FIG. 16. In this position, the member 1601 ais tucked behind the tooth 1603 in front of it so that the moveablemember 1601 does not interfere with the cutting operation. When thedangerous condition is detected, the moveable member may transition tothe deployed position, as shown by moveable member 1601 b in FIG. 16. Ascan be seen in FIG. 16, the deployed moveable member 1601 b may pivotabout the pivot point 1604 to extend in front of, and preferably beyond,the cutting member 1605 of the tooth 1603 when deployed. That way, thedeployed moveable member 1601 b will reduce the impact of the cuttingmember 1605 relative to the object being cut by the blade 14.

In various embodiments, the moveable members 1601 may comprise amagnetic material or a shape memory material (or alloy). For anembodiment using magnetic moveable members 1601, when the dangerouscondition is detected, the reaction system 32 may apply a magnetic fieldin the vicinity of the blade 14 to cause the magnetic moveable members1601 to deploy. In an embodiment employing shape memory materialmoveable members 1601, the reaction system 32 may activate the shapememory moveable members 1601, such as through heat or electricalcurrent, for example, to cause the moveable members 1601 to deploy. Inother embodiments, the moveable members 1601 may have other actuatingmeans, such as pyrotechnic charges, etc.

In another embodiment, as shown in FIG. 17, the blade 14 may comprisepivoting teeth members 1701. In such an embodiment, the pivoting teethmembers 1701 may be connected to the blade interior 1703 at a pivot1705. FIG. 17 shows a pivoting tooth member 1701 in the open or normalposition. In this position, the cutting instrument 1707 on the toothmember 1701 can cut effectively a workpiece being fed to the blade 14.When a dangerous condition is detected, the pivoting tooth member 1701pivots forward, counter-clockwise in FIG. 17, so that the cuttinginstrument 1707 is shielded completely or partially by the bladeperipheral portion 1709 in front of the pivoting tooth member 1701. Inthis embodiment, therefore, the pivoting tooth member 1701 rotates inthe direction that the blade 14 is spinning. In other embodiments, thepivoting teeth members 1701 could be configured to pivot or rotate inthe direction opposite the direction of rotation of the blade 14.

The pivoting teeth members 1701 may be actuated by an electricalcircuit, a pyrotechnic charge, or any other suitable means. In addition,in an embodiment where the blade 14 is braked, the stored rotationalenergy of the blade 14 may be sufficient to actuate the pivoting teethmembers 1701. In any event, the pivoting teeth members 1701 preferablymay be combined with another type of reaction system to mitigate thedanger of the spinning blade 14, even if the teeth have retracted to aless dangerous position. For example, a blade braking system or a bladedrop mechanism may also be employed.

In another embodiment, as shown in FIG. 18, the reaction system 32 mayactivate one or more visual and/or audible alarm systems when adangerous condition is detected by the detection system 30. For example,the reaction system 32 may be in communication, via wired and/orwireless data links, to the alarm system(s). Example alarm systems maycomprise warning light systems 1801 and audible alarm systems 1802 thatare in the building where the table saw 10 is located and/or in thetable saw 10 itself The audible alarm system 1802 may comprise aspeaker. The warning light system 1801 may comprise one or moreillumination devices, such as LEDs or lamps. Where wireless data linksare used, the data links between the reaction system 32 and the alarmsystems 1801, 1802 may be, for example, rf or infrared data links. Inone embodiment, the reaction system 32 may communicate with the alarmsystems 1801, 1802 using, for example, Powerline communication (PLC),Wi-Fi, Ethernet, or some other suitable communication standard. Inaddition, the reaction system 32 may be in communication with anautomated call center 1803, which may place an automated call when thedangerous condition is detected. For example, the automated call centermay place an automated call to an emergency response center (i.e.,9-1-1), relevant supervisors, or employees of the shop where the powertool 10 is located, etc. In addition, automatic text messages, e-mails,instant messages, etc. may be placed to supervisors, etc. when thedangerous condition is detected, according to various embodiments.

In another embodiment, the reaction system 32 may comprise an air bag1901, as shown in FIGS. 19 a-b. In one embodiment, the air bag, when itis in a non-deployed condition, may be stored in or under the throatplate 1902 that surrounds the blade 14 on the tabletop 12. When thedangerous condition is detected, the reaction system 32 may actuate theair bag 1901, as shown in FIG. 19 b. The air bag 1901 may be inflatedusing, for example, a solid propellant that burns extremely rapidly tocreate a large volume of gas to inflate the bag 1901, much like an airbag in automobiles. In other embodiments, a canister of compressed gasmay be used to inflate the air bag 1901 in response to detection of thedangerous condition. Activation of the air bag 1901 in response todetection of the dangerous condition may cause objects that are in thevicinity of the blade 14 to be knocked away from the blade 14. Inaddition or alternatively, an air bag could be positioned under thetabletop 12 at the side of the table saw 10 where an operator normallystands to operate the table saw 10. When activated in response todetection of the dangerous condition, such an air bag may push theoperator away from the tabletop 12 and the blade 14. In addition oralternatively, the operator may wear an air bag, such as on a braceletor belt, that is activated by the reaction system 32. In suchembodiments, the wearable air bag may have a wired or wirelessconnection to the reaction system 32. Deployment of such a wearable airbag may knock the operator and attached extremities thereof away fromthe tabletop 12 and/or blade 14.

In another embodiment, as shown in FIG. 20, the reaction system 32 maycomprise a magnetorheological (MR) rotary brake 2001 to brake the blade14 in response to detection of a dangerous condition by the detectionsystem 30. The MR rotary brake 2001, as shown in FIG. 20, may comprise arotor 2003 fixed to the shaft 2006 that rotates the blade (not shown).The shaft 2006 is placed in a bearing 2005 and can rotate in relation toa housing 2004 for the MR rotary brake 2001. Wires 2010 are connected,and supply electrical current, to a coil 2002. Between the rotor 2003and the housing 2004 there may be a spacing 2007 that is filled with MRfluid 2008. The MR fluid 2008 in the gap or spacing is physically nearthe coil 2002 such that when the coil 2002 is energized by electricalcurrent from the wire 2010, in response to detection of a dangerouscondition, the magnetic field from the coil 2002 causes the MR fluid togreatly increase its apparent viscosity to the point of becoming aviscoelastic solid, thereby braking the rotor 2003, which brakes theshaft 2006, which brakes the blade 14 (not shown) connected to the shaft2006. That is, for example, when a dangerous condition is detected bythe detection system 30, the detection system 30 may output a controlsignal to a current supply connected to the coil 2002. In response tothe control signal from the detection system 30, the current supply maybe coupled to the coil 2002 to energize the coil 2002. Such a MR brakereaction system could be combined, for example, with a blade dropmechanism.

In other embodiments, a MR clutch could be used to disengage the bladedrive mechanism. For example, in normal operating conditions, the MRfluid in the clutch could be energized by an electromagnetic field tocreate a friction lock to couple the drive mechanism to the blade. Whena dangerous condition is detected, the electromagnetic field is removed,causing the MR fluid to convert to its fluid state, effectivelydisengaging the drive mechanism from the blade.

In various embodiments, the table saw 10 may have numerous operatingmodes, including “on,” “off,” and “maintenance.” An operator of thetable saw 10 may transition between the modes using switches, such asone three-state switch for each of the modes, or a plurality of switchesthat provide similar functionality. According to various embodiments,the table saw 10 may undergo automated procedures, as shown in FIG. 21A,when the table saw transitions to various modes. If the table saw 10transitions to the Off mode (e.g., the operator flips the on/off switchto the off position), the table saw may take the following actionsautomatically: (i) the blade 14 retracts below the tabletop 12; (ii) thepower to the motor 14 is cut; and (iii) the reaction system 32 is turnedoff These steps may be performed in various orders, although preferablythe reaction system 32 should be turned off last. If the table saw 10transitions to the On mode, the table saw may take the following actionsautomatically: (i) the power to the motor 40 is turned on; (ii) thereaction system 32 is turned on; and (iii) the blade 14 is raised.Again, these steps may be performed in various orders, althoughpreferably the reaction system 32 is turned on prior to the raising ofthe blade. A processor-based controller 2120, as shown in FIG. 21B, maycontrol and initiate these automatic reactions. An automated, motorizedblade height adjustment system 2122 may be used to raise and lower theblade height in such table saws. If the table saw 10 transitions to themaintenance mode, such as if the operator hits the “maintenance” buttonor switch 2124 in order to change the blade, for example, the reactionsystem 32 is turned off Also, the controller 2120 may output a signal tothe motor control circuit 2130 to turn the motor 40 on or off Otherconvenience and safety features may be provided or monitored in themaintenance mode. For example, a sensor may detect whether the nutholding on the blade is over-torqued or not. Also, in the maintenancemode, the blade drive shaft may be automatically locked to aid in theblade removal process.

As an alternative to automated blade height adjustment system, sidepanels in the tabletop 12 may rise automatically to surround the blade14 when the saw is turned off. Also, the throat plate 13 (see FIG. 1)could rise automatically to surround the blade when the saw is turnedoff

FIG. 22 shows an embodiment of a system that may be used to stop theblade 14 when the saw 10 is turned off As shown in FIG. 22, the systemmay include a clutch 2201 that couples the motor 40 to the blade shaft2202. The illustrated embodiment shows a direct drive for the blade 14,although a belt drive or gear drive could be used to power the blade 14as well. The system also includes a brake system 2204 that, whenactuated at turn off of the saw 10, grips an interior portion of theblade 14 to stop the blade 14 from spinning, preferably in a manner thatis not destructive to the blade 14. That way, when the saw 10 is turnedoff, the clutch 2201 may disengage the motor 40 from the blade 14, andthe brake system 2204 may stop the blade 14 from spinning. Such anembodiment effectively eliminates the need to detect whether the blade14 is still spinning after the motor 40 is cut in order to keep thereaction system 32 enabled because the blade 14 is braked by the brakesystem 2204 immediately at turn-off. Alternatively, some of the bladespin-down detection mechanisms described herein could be used to detectblade spin down to keep the reaction system 32 active and armed,although spin down detection techniques based on the motor 40 will notbe effective in such an embodiment because the power to the motor iscut.

According to various embodiments, it may be desirable to know theconductivity of the wood or other workpiece being cut by the table sawand adjust detection systems accordingly. For example, in a capacitivedetection system the baseline current and/or voltage drawn from theblade 14 during normal operations (e.g., when the blade is in contactwith the workpiece, but not in contact with a foreign object) may dependon the conductivity of the workpiece. Some other types of detectionsystems may also utilize the conductivity of the workpiece to determinewhen the blade has come into contact with a foreign object.

FIG. 23 illustrates one embodiment of a table saw 10 having aconductivity sensor 2302 for measuring the conductivity of a workpieceto be cut by the blade 14. The conductivity sensor 2302 may provide tothe detection system 30 a signal indicative of the conductivity of theworkpiece being cut (or to be cut). The detection system 30 may compriseone or more processors for receiving and processing the signal from thesensor 2302. The detection system 30 may process the conductivity datafrom the sensor 2302 in determining whether a foreign object has comeinto contact with the blade 14. For example, if the workpiece has a highconductivity, its electrical behavior in contact with the blade may becloser to that of a human body part: Accordingly, the detection system30 may adjust its sensitivity and/or disable capacitive foreign objectsensing. For example, the saw 10 may instead use other foreign objectsensing mechanisms including, for example, those discussed herein below.In addition, the detection system may provide an alert (e.g., a visualor audible alert) to the user that the workpiece has a highconductivity.

The conductivity sensor 2302 may be physically embodied as one or moresensors that may be placed at various locations on the saw 10. Forexample, FIG. 24 illustrates one embodiment of the table saw 10 with atrailing edge sensor assembly 2408. The blade 14 of the table saw 10 isshown in contact with a workpiece 2406, which may be moved across thetable saw 10 in the direction indicated by arrow 2404. After being cutby the blade 14, the workpiece 2406 may contact the sensor assembly2408. The sensor assembly 2408 may include any suitable type of sensorfor measuring the conductivity of the workpiece 2406. For example, thesensor assembly 2408 may include one or more probes made of a conductivematerial positioned to contact the workpiece 2406 after it has been cutand fed past the blade 14. The probes may be used to cause a current toflow through the workpiece 2406. The voltage drop across the workpiece2406 may then be used to determine its conductivity. Any suitableassembly may be used to bring the sensors into operational contact withthe workpiece 2406. For example, as illustrated in FIG. 24, the sensorassembly 2408 may comprise a wheel 2410 positioned behind the blade 14.The wheel 2410 may be slightly narrower than the kerf of the blade 14,allowing the wheel 2410 to fit within the cut to the workpiece 2406 madeby the blade 14. The wheel 2410 may comprise spikes (or probes) 2412that protrude towards the workpiece 2406. As the wheel 2410 passesthrough the cut in the workpiece 2406, the spikes 2412 may come intocontact with the portion of the workpiece 2406 that has just been cut bythe blade 14. The spikes 2412 may be, or may comprise, sensor leads formeasuring the conductivity of the workpiece 2406. Sensing theconductivity of the workpiece 2406 within a fresh cut may give a readingthat is indicative of the interior of the workpiece 2406.

FIG. 25 illustrates another embodiment of the table saw 10 where theconductivity sensor 2302 comprises a leading edge conductivity sensorassembly 2504 positioned at the front or leading edge of the blade 14.No workpiece is shown in FIG. 25. In use, however, a workpiece would bemoved towards the front or leading edge of the blade 14 in the directionof arrow 2507. The sensor assembly 2504 is illustrated upstream of theblade 14. The sensor assembly 2504 may comprise one or more spikedwheels 2506. The wheels 2506 may be configured to rotate about an axisparallel to the arbor 38 of the blade 14. The spikes on the wheels 2506may come into contact with the workpiece before it contacts the blade14. The spikes may be, or may comprise, leads for conductivity sensorsfor sensing the conductivity of the workpiece. In some embodiments, thespikes may be sharp, allowing them to slightly puncture the exterior ofthe workpiece and provide a conductivity reading from below the surfaceof the workpiece. According to various embodiments, one or more wheels2506 on the table saw 10 may be adjustable along their axis of rotation.This may allow an operator of the table saw 10 to adjust the wheels 2506based on a width of the workpiece.

FIG. 26 illustrates one embodiment of the table saw 10 where the sensor2302 comprises a sensing table top surface 2604. The surface 2604 maycomprise a metallic or other conductive material. When the surface 2604is in contact with a workpiece (not shown), a current may be passedthrough the workpiece to measure its conductivity. According to variousembodiments, an operator of the table saw 10 may place the workpiece onthe surface 2604, allowing the saw 10 to measure the conductivity of theworkpiece prior to or during a cut. FIG. 27 illustrates one embodimentof the table saw 10 where the sensor 2302 comprises a sensing surface2704 that is less than all of its table top 2706. The sensing surface2704 may be positioned upstream of a blade 14 as shown in FIG. 27, or inother embodiments it could be located at different locations of thetabletop including at a trailing edge of the blade 14. The sensingsurface 2704 may operate according to principles similar to that of thesurface 2604 described above. In use, a workpiece (not shown) may bebrought into contact or proximity with the sensing surface either as theworkpiece is pushed towards the blade 14 or before a cut is begun. Thissensing surface 2704 may sense the conductivity of the workpiece andadjust the operation of the detection system 30 and/or the reactionsystem 32 accordingly. The sensing surface 2704 may be electricallyinsulated from the rest of the tabletop 12.

According to various embodiments, the conductivity sensor 2302 maycomprise all or a portion of a blade 14 of the table saw 10. Inembodiments that monitor changes in the blade capacitance to determinewhether a foreign object is in contact with the blade, it may not bedesirable to use the entire blade 14 to detect the conductivity of aworkpiece. FIG. 28 illustrates one embodiment of a segmented blade 2802that may be used both to detect the conductivity of a workpiece and tocapacitively detect foreign objects in contact with the blade. The blade2802 in such embodiments may comprise conductive sensing teeth 2804 andcapacitive sensing teeth 2808 at different regions of the blade 14.Although the respective teeth 2804, 2808 are shown in contiguoussections in FIG. 28, it will be appreciated that they may beinterspersed around the blade 2802 in any suitable pattern. Theconductive sensing teeth 2804 and capacitive sensing teeth 2808 may beelectrically insulated from one another and placed in a separate circuitpaths.

In use, the capacitive sensing teeth 2808 may be used by the detectionsystem 30 to determine whether a foreign object is in contact with theblade 2802. For example, the detection system 30 may monitor a change inan electrical signal applied to the capacitive sensing teeth 2808 due toa change in capacitance in the teeth 2808 caused by contact with aforeign object. The conductive sensing teeth 2804 may be used as aconductivity sensor, or a portion thereof. For example, all or part ofeach conductive sensing tooth 2804 may serve as a probe. An additionalprobe (not shown) may be otherwise placed in contact with the workpiece.For example, the operator may secure the additional probe to theworkpiece. In various embodiments, the additional probe may be embeddedin the saw's table top. Also, according to various embodiments, anadjacent or other nearby conductive sensing tooth 2804 may serve as theadditional probe. In use, a current may be passed from the firstconductive sensing tooth 2804, through the workpiece and through thesecond conductive sensing tooth 2804. The voltage drop in the signal maybe indicative of the resistance and/or conductivity of the workpiece.Because the blade 2802 may measure the conductivity of material that itis in contact with, it may be used to detect contact between the bladeand a foreign object. For example, if the blade 2802 senses a largeincrease in the conductivity of the materials in contact with the blade2802, it may indicate that a foreign object, such as a conductive bodypart, is in contact with the blade 2802. In such situations, thedetection system 30 may trigger the reaction system 32.

In the embodiment described in FIG. 2, the blade 14 acts as one elementof a capacitor. The excitation plate 34 is separated from the blade 14by a dielectric (e.g., air) and serves as a second element of thecapacitor. FIGS. 29 and 30, however, illustrate one embodiment of ablade 2900 that serves as a complete capacitor. The blade 2900 comprisesa blade body 2902, a plate 2904, and a dielectric 2906. The blade body2902 may comprise the teeth 2908 of the blade 2900, and may also definea hollow cavity 2910 for receiving the dielectric 2906 and the plate2904. Within the cavity 2910, the dielectric 2906 may be positionedbetween the blade body 2902 and the plate 2904 and may cause electricalinsulation of the body 2902 and plate 2904. In this way, the blade body2902 and plate 2904 may serve as elements of a capacitor. When the blade2900 is used in a detection system, such as the detection system 30described above, the excitation plate 34 may be omitted. Instead, theexcitation voltage may be driven onto the blade body 2902 via thecapacitor plate 2904. The capacitor plate 2904 may be connected to avoltage drive source via a connection through the blade shaft that isinsulated from the shaft and the blade body 2902. Because the blade 10itself makes up the entire capacitor, its capacitance may be more easilyset during manufacture. In contrast, the capacitance of the blade 14 andexcitation plate 34 capacitor described above is dependent on variousunpredictable environmental conditions, and therefore, its capacitanceat any given time may be difficult to control or adjust. For example,the dielectric 2906 may be selected to achieve a desirable bladecapacitance. Also, the surface area of the body 2902 and the plate 2904may be manipulated. Manipulating the blade capacitance may lead tosuperior detection performance as well as an improved signal-to-noiseratio.

FIG. 31 illustrates one embodiment of a blade 3100 comprising aplurality of blade whiskers 3102 radiating generally from the center ofthe blade 3100. The blade 3100 may be used with any saw having adetection system, such as the saw described in FIG. 2 above. The bladewhiskers 3102 may extend radially from the blade 3100, creating acontact radius beyond the teeth 3104. In one example embodiment, thewhiskers 3102 may extend up to about 1 mm beyond the teeth 3104. In thisway, a foreign object contacting the blade 3100 may contact the whiskers3102 before contacting the teeth 3104. The whiskers 3102 may be shortenough to avoid wrapping around a foreign object, such as the finger ofan operator, and thus pulling it into the blade 3100. According tovarious embodiments, the whiskers 3102 may be electrically conductiveand electrically coupled to all or a portion of the blade 3100. When theforeign object contacts the whiskers 3102, the capacitance, and thus thesignal drawn from the blade 3100, may begin to change. Because thischange begins to occur before the foreign object contacts the teeth 3104of the blade 3100, the effective reaction type of the saw may beimproved. According to various embodiments, the length of the whiskers3102 may be selected based on the reaction type of the detection andreaction systems of the saw 10. For example, if the typical reactiontime of the saw 10 without the whiskers 3102 results in a cut 0.6 mm indepth, then the whiskers may be 0.6 mm or longer to prevent any cut inthe event of a foreign object contacting the blade.

When the blade 3100 is used to cut a workpiece, the whiskers 3102 may bedesigned to bend or retract out of the path of the teeth 3104. In thisway, the teeth 3104 may cut the workpiece without interference from thewhiskers 3102. The whiskers 3102 may be made, for example, from a metalwire (e.g., steel, aluminum, etc.). Also, for example, the whiskers 3102may be made from a conductive carbon composite or other electricallyconductive material. According to various embodiments, the whiskers 3102may comprise a non-capacitive sensor. For example, each whisker 3102 maycomprise one or more probes for measuring the conductivity of materialsin contact with the blade 3100. Also, according to various embodiments,the blade 3100 may include a mechanism for replenishing the length ofthe whiskers 3102. In use, individual whiskers 3102 may be broken ortorn as they contact the workpiece. Accordingly, one or more of thewhiskers 3102 may comprise a reel (not shown) of additional whiskermaterial. The reel may be actuated by centripetal force to extendadditional whisker material when its corresponding whisker 3102 is lostor shortened.

FIG. 32 illustrates a diagram of one embodiment of a segmented blade3200 that may be used with the saw embodiment shown in FIG. 2. The blade3200 is shown in the process of cutting a workpiece 3210. Arrow 3212indicates the direction of movement of the workpiece 3210 relative tothe blade 3200. Arrow 3214 indicates the rotation direction of the blade3200. In FIG. 32, the blade 3200 is shown with four electricallyinsulated segments 3202, 3204, 3206, 3208. Each of the segments 3202,3204, 3206, 3208 may form a capacitor (e.g., in conjunction with anexcitation plate 34 and/or utilizing a laminate design such as describedabove with respect to FIGS. 29 and 30). Because the segments areelectrically insulated, each capacitor (e.g., each blade segment 3202,3204, 3206, 3208) may be capable of being separately monitored by thedetection system 30.

As the blade spins, each of the segments 3202, 3204, 3206, 3208 isalternately in contact with a leading portion of the workpiece 3210 (inFIG. 32, segment 3204), a trailing portion of the workpiece 3210 (inFIG. 32, segment 3202) and no portion of the workpiece (in FIG. 32,segments 3206 and 3208). The capacitance of each segment (e.g., asmeasured by an excitation current and/or voltage) may reflect theproperties of the material in contact with the respective segment. Thismay enable a variety of useful features. For example, the segmentedblade 3200 may enable the detection system 30 to re-calibrateon-the-fly. Portions of the blade cycle where a given segment 3202,3204, 3206, 3208 is not in contact with the workpiece 3210 may be usedas baseline measurements for recalibration of the segment. Also, forexample, the detection system 30 may be able to track whether the saw isat the beginning, middle, or end of a cut. This may allow the detectionsystem 30 to calibrate its sensitivity accordingly. Also, use of theblade 3200 may allow the detection system to compare differences inproperties between the leading portion and the trailing portion of theworkpiece 3210.

FIG. 33 illustrates one embodiment of the table saw 10 having anoverhead sensor assembly 3304. The overhead sensor assembly 3304 maycomprise one or more sensors, which may be active or passive. Forexample, an active sensor may comprise an emitter as well as a receiver.Sensors that are passive may not comprise an emitter. According tovarious embodiments, the transmitter and receiver may be separate, withone or both of them located on the saw 10 at a location different fromthe overhead sensor assembly 3304. When the saw 10 is in use, its blade3302 and a workpiece 3308 may be in the field of view of at least one ofthe sensors of the sensor assembly 3304.

According to various embodiments, the sensor assembly 3304 may comprisea radar sensor. A radar sensor may comprise an emitter that generateselectromagnetic waves (e.g., radio waves, microwaves, etc.) and directsthe electromagnetic waves toward the blade 3302. The waves may reflectoff of the blade 3302, the workpiece 3308 and any foreign objects thatmay be present. A receiver may sense the reflected waves and provide anoutput signal to a processor-based detection system 30. The detectionsystem 30 may glean various information from the input signal about thereflected waves. For example, the reflected waves may provide anindication of the direction and speed with which the workpiece 3308 ismoving relative to the blade. If the workpiece 3308 reverses its motion,that may indicate a kickback event, which may cause the detection system30 to activate the reaction system 32. If a foreign object is detectedwithin a predetermined distance from the blade 3302, then a reactionsystem 32 may be activated. For example, if a foreign object is detectedbetween the blade 3302 and the sensor assembly 3304, the reaction system32 may be activated by the detection system 30. More details regarding aradar sensing system may be found in U.S. Pat. No. 7,421,932, which isincorporated herein by reference in its entirety.

According to various embodiments, the sensor assembly 3304 may comprisean infrared (IR) receiver. The IR receiver may sense the IR signature ofthe blade 3302, the workpiece 3308, and any foreign objects present inits field-of-view. The IR signature of the blade 3302 and workpiece 3308may be distinguishable from the IR signature of a body part or otherforeign object that may inadvertently come near the blade. The detectionsystem 30 may monitor the output of the IR receiver. If the IR receiverindicates that a foreign object is within a predetermined distance fromthe blade 3302, a reaction system may be activated. For example, if aforeign object is detected between the blade 3302 and the sensorassembly 3304, the reaction system 32 may be activated.

In other embodiments, the sensor assembly 3304 may include emitters andreceivers for measuring backscatter off of the blade 3302, the workpiece3308 and any foreign objects that may be present near-by. Any suitablefrequency of electromagnetic radiation may be used to measurebackscatter. According to various embodiments, however, a frequency orfrequencies may be selected based on the difference in backscatterprofiles between typical workpieces 3308 and typical foreign objects,such as human body parts. In use, backscatter techniques may be able todifferentiate between workpieces 3308 and foreign objects. For example,a foreign object, such as the skin on a body part, may scatter back afirst quantity of radiation, while a workpiece 3308 of the same surfacearea may scatter back a second quantity of radiation. This may allow thedetection system 30 to differentiate between the two. If a foreignobject is detected within a predetermined distance of the blade 3302(e.g., if the foreign object is over the blade 3302 or between the blade3302 and the sensor assembly 3304), then the reaction system 32 may beactivated by the detection system 30, which is in communication with thesensor assembly 3304.

In some embodiments, the sensor assembly 3304 may include an opticalcamera (e.g., a CCD camera). The optical camera may have a resolutionfine enough to allow it to determine a distance between a foreign objectand the blade 3302. If the distance is less than a predetermined amount,the reaction system 32 may be triggered by the detection system 30.Various image processing algorithms may be used by the detection system30 to distinguish the blade, a typical workpiece, and a foreign object.

In various embodiments, the sensor assembly 3304 may include an emitterand receiver for measuring differential reflection. Differentialreflection may be a measure of difference in reflection betweensurfaces. For example, a foreign object may reflect more or lesselectromagnetic radiation as compared to a typical workpiece 3308 and/orthe blade 3302. The emitter for differential reflection may be anysuitable emitter of electromagnetic waves including, for example, alaser. The detection system 30 is in communication with the sensorassembly 3304 and determines whether the reaction system 32 should betriggered based on the differential reflection detected by the sensorassembly 3304.

FIGS. 34-42 illustrate embodiments utilizing downstream safety members(e.g., safety members that are positioned near the trailing or rear edgeof the blade 14). A downstream safety member is a component of a tablesaw that is positioned parallel to and downstream from the blade 14.Specific examples of downstream safety members include riving knives andsplitters. Different downstream safety members may serve differentpurposes, for example, as described herein. Generally, a downstreamsafety member may serve to steady a workpiece and/or to mitigate therisk of a kickback event by preventing a cut from closing around theblade 14.

FIG. 34 illustrates one embodiment of a downstream safety member 3400having directional snells 3402. The snells 3402 may extend outwardly atan angle from the downstream safety member 3400. The snells 3402 may beconfigured so that a workpiece may smoothly pass over the snells 3402 inthe downstream direction, but is impeded if the workpiece is kicked-backin the upstream direction. FIG. 35 illustrates a top view of thedownstream safety member 3400. A workpiece 3406 is illustrated beingpushed downstream, as indicated by arrow 3408. When the workpiece 3406contacts the snells 3402 moving downstream, it may slide along thesnells 3402 without significant resistance because the snells arepointed generally away from the blade and in the direction that theworkpiece is being fed. In the event of a kickback, however, theworkpiece 3406 may be thrust upstream. In this case, the snells 3402 maydig into the workpiece 3406, either preventing the workpiece from movingupstream or impeding its upstream motion.

The snells 3402 may take any suitable form and may be made of anysuitable material (e.g., steel, another suitable metal, engineeredplastic, etc.). For example, in various embodiments, the snells 3402 maybe flexible flaps formed into or secured to the downstream safety member3400. When the workpiece 3406 passes in the downstream direction, theflaps may flex, allowing the workpiece 3406 to pass. When the workpieceis thrust upstream, the flaps may not flex and may instead dig into theworkpiece 3406, impeding its upstream movement. According to variousembodiments, the snells 3402 may be actuatable by the reaction system32. For example, each snell 3402 may be extendible from a rest position,where the workpiece 3406 is allowed to pass without significantresistance, to an extended position, where the motion of the workpiece3406 is impeded. When a kickback condition is detected, the reactionsystem 32 may extend the snells 3402 to prevent the workpiece 3406 frombeing thrust back towards the operator and/or the blade 14. The snells3402 may be actuated according to any suitable mechanism. For example, amass of nitinol or another shape memory allow may be actuated to lifteach snell 3402 to the extended position. In other embodiments, eachsnell 3402 may be spring loaded from the rest position to the extendedposition. In still other embodiments, the snells 3402 may be extendedusing solenoids, pneumatics, hydraulics, magnets, pyrotechnics, or anyother suitable method.

FIGS. 36-38 illustrate one embodiment of the table saw 10 including adownstream safety member 3602 comprising one or more wing members 3604.The wing members 3604 may extend roughly parallel to the table surface3614 and roughly perpendicular to a body 3608 of the downstream safetymember 3602. A workpiece 3610 being acted upon by a blade 14 may passunder the wing members 3604 when extended. In this way, the wing members3604 may serve to prevent the workpiece 3610 from lifting off of thetable surface. This may prevent and/or mitigate a kickback event. Duringa typical kickback event, the motion of the workpiece 3610 relative tothe blade 14 is stopped or slowed (e.g., when the blade 14 contacts aknot or hard portion of the workpiece 3610, by a pinching off of the cutbehind the blade 14, etc.). When the workpiece 3610 is stopped orslowed, the motion of the blade 14 pushes the workpiece 3610 up, whereit contacts the top of the blade 14 and is thrust back towards theoperator. Wing members 3604 may prevent or mitigate a kickback event bypreventing the workpiece 3610 from riding upwards relative to the blade14.

According to various embodiments, the wing members 3604 may be movablefrom a resting position to a deployed position when triggered, such asby turn-on of the motor/blade. In the resting position, the wing members3604 may be parallel to a body 3608 of the downstream safety member3602. In some embodiments, the combined width of the body 3608 and thewing member or members 3604 may be less than the kerf of the blade 14,allowing the downstream safety member 3602 to pass through the cut inthe workpiece formed by the blade 14 if the wing members 3604 are in theresting position. Normally, the wing members 3604 are deployed when thesaw is being operated. FIGS. 36 and 37 illustrate one embodiment wherethe wing members 3604 fold down against the body 3608 of the downstreamsafety member 3602 when in the resting position. FIG. 38 illustratesanother embodiment where the wing members 3604 fold upwards when in theresting position. In such an embodiment, the wing members 3604 maytransition to the deployed position, parallel to the tabletop whentriggered by a kickback detection system. According to variousembodiments the downstream safety member 3602 may comprise a heightadjustment mechanism 3616 for raising and lowering the downstream safetymember 3602. This may allow an operator to adjust the height of the wingmembers 3604 based on the height of the workpiece 3610.

According to various embodiments, the downstream safety member 3602 maybe actuated from the resting position to the deployed position by thereaction system 32 upon detection of a kickback event by the detectionsystem 30. The kickback event may be sensed according to any suitablemethod including, for example, those described herein below. Upondetection of the kickback event, the reaction system 32 may cause thewing members 3604 to be transitioned, such as from the upright restingposition shown in FIG. 38, to the deployed position using any suitablemechanism or method. For example, the wing elements 3604 may be actuatedby a spring element, solenoids, pneumatics, hydraulics, pyrotechnics,etc.

According to various embodiments, a downstream safety member can be usedas a component of the reaction system 30. For example, the downstreamsafety member may be used to cover the exposed portion of the blade 14or otherwise prevent or stop contact between the blade 14 and a foreignobject. FIGS. 39 and 40 illustrate one embodiment of the table sawhaving a downstream safety member 3904. The downstream safety member3904 has a resting position, shown in FIG. 39, and a deployed position,shown in FIG. 40. In the resting position, a portion of the downstreamsafety member 3904 may extend above the table top 3906 and serve as astandard downstream safety member, such as a splitter.

The detection system 30 may detect a dangerous condition according totechniques described herein, including contact between the blade 14 anda foreign object or proximity of the foreign object to the exposedportion of the blade 14. When the condition is detected, the detectionsystem 30 may trigger the reaction system 32. The reaction system 32may, in turn, trigger an actuating mechanism 3910, which may rapidlytransition the downstream safety member 3904 from the resting position,shown in FIG. 39, to the deployed position, shown in FIG. 40. In thisway, the safety member 3904 may prevent the foreign object fromcontacting the blade 14, or if the foreign object has already contactedthe blade 14, the safety member 3904 may push or knock the foreignobject away from the blade 14.

The downstream safety member 3904 may be transitioned from the restingposition to the deployed position according to any suitable actuationmechanism or method. In some embodiments, the saw may include tracks(not shown) for directing the downstream safety member 3904 from theresting position to the deployed position. The actuating mechanism 3910may comprise any suitable mechanism for moving the safety member 3904along the tracks including, for example, spring loading, pneumatics,hydraulics, explosive charges, etc. Also, in some embodiments, thedownstream safety member 3904 may be directed from the resting positionto the deployed position by a series of pivotable bar members (notshown). In these embodiments, the actuating mechanism 3910 may beconfigured to pivot the downstream safety member 3904 about the barsagain using any suitable mechanism (e.g., spring loading, pneumatics,hydraulics, pyrotechnics, etc.).

FIG. 41 illustrates another embodiment of the saw 10 having a downstreamsafety member 3952 that may be used as part of a reaction system 32.Upon detection of a triggering condition involving a foreign object andthe blade 14 by the detection system 30, the downstream safety member3952 may be split into two or more sections. The actuating mechanism3910 may propel a first section along track 3958, and a second sectionalong track 3956. As shown in FIG. 41, the tracks may run generallyparallel to the blade 14 on opposite sides of the blade 14. In this way,the downstream safety member 3952 may cover the blade 14 to preventand/or mitigate contact between the blade 14 and a foreign object. Insome embodiments, the downstream safety member 3952 may not split intwo, but instead the entire downstream safety member 3952 may bepropelled down a track on one side of the blade 14. The actuatingmechanism 3910 may utilize any suitable propelling mechanism including,for example, spring loading, pyrotechnics, solenoids, pneumatics,hydraulics, etc.

FIG. 42 illustrates one embodiment of a saw 10 having a downstreamsafety member 4202 with a material sensor 4204 thereon. The materialsensor 4204 may be any suitable type of sensor for sensing a property ofa workpiece (not shown). For example, the sensor 4204 may be aconductivity sensor for sensing the conductivity of the workpiece which,as described above, may be an indicator of its moisture content. Thesensor 4204 may be positioned at any suitable location on the downstreamsafety member 4202, and may take any suitable physical form. Forexample, the sensor 4204 may include probes that extend perpendicularlyfrom the downstream safety member 4202 to contact material within a cuton a workpiece created by the blade 14. The sensor 4204 may be incommunication with the detection system 30 in a manner similar to thatdescribed above with respect to FIG. 23.

In some table saws, the blade height is manually adjustable, such as byusing a crank. An operator of the table saw may adjust the blade heightto match the height of the workpiece being cut. Many operators, however,neglect to adjust the blade height for each cut. Instead, operatorssometimes set the blade to a height that is high enough to allow them tocut a number of workpieces. As a result, the blade is sometimes too highfor certain cuts, creating a potentially unsafe condition. FIG. 43illustrates a block diagram of a table saw 4300 with an automaticallyadjustable blade 14. The blade 14 may be adjustable with a mechanicaladjustment mechanism 4320. The mechanism 4320 may be any suitable typeof mechanism including, for example, known manual blade heightadjustment mechanisms. The mechanism 4320 may be powered by an actuatingmechanism 4321, such as a stepper motor or other suitable device. Aheight sensor 4324 may be used to sense the height of the workpiececurrently being cut by the blade 14. The sensor 4324 may be any suitabletype of sensor including, for example, an optical sensor. The sensor4324 may be positioned so that it can measure the height of workpiecesat a location in front of the leading edge of the blade 14. The heightsensor 4324 may provide an output signal indication of the height of theworkpiece to a processor-based height adjustment circuit 4322. From theoutput signal of the sensor 4324, the circuit 4322 may determine theheight of the workpiece and whether the blade height needs to beadjusted or not given the height of the workpiece. The circuit 4322 maythen signal the actuating mechanism 4321 to adjust the mechanism 4320 toraise or lower the blade 14 based on the height of the workpiece. Forexample, the blade 14 may be raised such that its top is a predetermineddistance above the top of the workpiece. In some embodiments, the bladeheight adjustment mechanism 4320 may also raise or lower the motor 40 aswell.

FIGS. 44-46 illustrate one embodiment of the table saw 10 according toother embodiments. The blade 14 and table top surface 4304 are shown inFIGS. 44-46. The height sensor 4324 may comprise a fan emitter 4308 anda detector array 4306 (shown in FIG. 44). The fan emitter 4308 may emita laser or other electromagnetic beam across the table top 4304 andworkpiece 4307 towards the detector array 4306. The beam may be ‘fanned’or shaped to disperse vertically. When the workpiece 4307 breaks thebeam, a portion of the beam may be prevented from reaching the sensorarray 4306. Based on the portion of the beam that reaches the detectorarray 4306, the height adjustment circuit 4322 may determine the heightof the workpiece and send appropriate signals/instructions to theactuating mechanism 4321. FIGS. 45 and 46 illustrate the operation ofthe saw 10 with two workpieces, 4307′ and 4307″. As shown in FIG. 45,the workpiece 4307′ has a first height. In FIG. 45, the blade 14 isshown relative to the table top 4304 at a height roughly correspondingto that of the workpiece 4307′. As shown in FIG. 46, the workpiece 4307″has a second height that is greater than that of the workpiece 4307′.Accordingly, FIG. 46 shows the blade 14 at a greater height relative tothe tabletop than is shown in FIG. 45. The height of the blade 14relative to the tabletop in FIG. 46 may roughly correspond to the heightof the workpiece 4307″.

Various embodiments of the present invention are also directed toretrofitting existing table saws with detection and reaction systems.FIG. 47 illustrates one embodiment of the saw 10 with a retrofit package4702 installed. The retrofit package 4702 may comprise a detectionsystem 30, a reaction system 32 and a power system 4704. The detectionsystem 30 may be any suitable type of detection system including, forexample, those described herein. For example, in one embodiment, theretrofit package 4702 may comprise an excitation plate 34 that isinstalled next to the blade 14, as shown. The detection system 30 maydrive a signal onto the excitation plate and monitor changes in theresulting blade current or signal due to changes in the capacitancebetween the blade 14 and the plate 34 to detect contact between theblade 14 and a foreign object. In some embodiments, the blade 14 may bereplaced with a blade that does not require an excitation plate such as,for example, blade 2900 described herein. Other non-capacitive detectionsystems 30 may be used including, for example, the radar, backscatter,and/or video-based embodiments described herein.

The reaction system 32 may comprise any suitable type of reactionmechanism. According to various embodiments, however, reaction systems32 requiring a minimum of modification to the saw 10 may be selected.Examples of such systems include those utilizing actuatable throatplates, actuatable table tops, airbags, changes to the blade shape,blade brakes, etc. The reaction system 32 and detection systems 30 ofthe retrofit package 4702 may be powered by a power system 4704. Thepower system 4704 may comprise a connection to a power source of the saw10. According to various embodiments, the power system 4704 may comprisea blade-driven generator, such as those described with reference toFIGS. 5-6. In this way, the reaction and detection systems 32, 30 maycontinue to operate until the blade 14 completely spins down.

Operators of table saws sometimes use push sticks to guide or feed theworkpieces towards the blade. Use of a push stick may allow the operatorto keep their hands farther away from the blade 14 when feeding aworkpiece toward the blade 14. FIGS. 48 and 49 illustrate one embodimentof a push stick 4802 according to various embodiments of the presentinvention. The push stick 4802 may comprise a handle and an endeffector, separated by a shaft. The operator may grasp the push stick4802 by the handle and use the end effector to push the workpiece, asshown in FIG. 49. FIG. 50 illustrates a block diagram of the push stick4802 in communication with an example saw 4820. According to variousembodiments, the push stick 4802 may comprise one or more accelerometers4810. The accelerometer(s) 4810 may be in communication with atransmitter 4824, which may transmit signals indicative of theacceleration of the push stick 4802 to the saw 4820 (e.g., viareceiver/detector 4822). The detection system 30 of the saw 4820 maymonitor the acceleration of the push stick 4802, as this may beindicative of the acceleration of the workpiece 4804 and/or theoperator's hand. If the acceleration of the push stick 4802 fallsoutside of acceptable bounds, the detection system 30 may trigger thereaction system 32. For example, the acceleration of the push stick maybe outside of acceptable bounds if the stick accelerates too quickly inthe direction of the blade 14. In addition, a sudden acceleration awayfrom the blade 14 may indicate a kick back condition. The push stick4802 may also comprise devices and/or sensors allowing the detectionsystem 30 to estimate its location. For example, the push stick 4802 maycomprise a Radio Frequency (RF) transmitter 4812 that may periodicallytransmit RF pulses. The saw 4820 (e.g., via the detector/receiver 4822)may receive the RF pulses. Based on the strength of the RF pulses, thedetection system 30 may estimate the distance between the push stick4802 and the blade 14. In some embodiments, the push stick 4802 maycomprise an infrared (IR) pulse generator. The IR pulses may be receivedby the saw 4820. For example, the saw 4820 may comprise a plurality ofIR receivers positioned at different locations on the saw 4820. Thesemay allow the saw to use triangulation to estimate the position of thepush stick 4802 relative to the blade, for example.

FIG. 51 is a top view of a table saw 10 with a suction feed assembly5102 for feeding workpieces towards the blade 14 according to variousembodiments of the present invention. The suction feed assembly maycomprise a plurality of suction elements 5104 located on the table atthe leading edge of the blade 14. Each suction element 5104 may compriseone or more suction generated devices. When actuated, the suctiongenerating devices may create a vacuum between the section element 5104and any object in contact with the section element 5104 (e.g., theworkpiece). Each suction element 5104 may reciprocate towards and awayfrom the blade, for example, as shown by arrows 5106. Adjacent sectionelements 5104 may reciprocate 180° out of phase. Accordingly, thesuction elements 5104 may be selectively actuated and deactuated to movea workpiece towards or away from the blade 14. In this way, it may notbe necessary for an operator to place their hand near the blade 14.Instead, the suction elements 5104 may feed the workpiece toward theblade 14. The state of the feedback from the suction elements 5104 canbe used to detect hazardous conditions.

FIG. 52 illustrates a top-down view of one embodiment of a kick backdetection mechanism 5200. As shown in the illustrated embodiment, theblade 14 and arbor 38 may be mounted in a kick back frame 5202 that ispivotable relative to the remainder of the table saw about the joint5204. Arrow 5208 indicates the direction of movement of a workpiece. Thekick back mechanism 5200 may serve a variety of purposes. For example,many kickback conditions occur when a cut is pinched or otherwiseknocked out of alignment, causing the cut portion of a workpiece tocontact a rear portion of the blade 14. Because the kick back mechanism5200 allows the blade 14 some freedom of motion around the pivot 5204,it may prevent many kickback conditions. In some embodiments, the kickback mechanism 5200 may comprise a sensor (not shown) positioned tosense movement of the kick back frame 5202 about the joint 5204. Thesensor may be in communication with the detection system 30. Movement ofthe kick back frame 5202 about the joint 5204 may indicate a kickbackcondition. Accordingly, when the detection system 30 receives a signalfrom the sensor indicating that greater than a predetermined amount ofmotion has occurred about the joint 5204, it may trigger a reactionsystem 32. FIG. 53 illustrates an alternative embodiment of the kickback mechanism 5200′. With the mechanism 5200′, the blade 14 and arbor38 are mounted to a four-bar linkage frame 5210, which is shown rigidlymounted to a portion 5214 of the saw. The four-bar linkage frame 5210may allow the blade 14 to move from side-to-side, as illustrated byarrow 5216. This may serve to prevent kickback conditions, as describedabove. Also, for example, a sensor may be positioned to sense movementof the linkage frame 5210, which, if greater than a predeterminedthreshold, may indicate a kickback condition. The sensor (not shown) maybe positioned at any location allowing it to sense movement of the frame5210, but may be positioned at one of the joints 5212 of the frame 5210.In another embodiment, strain measurements, from a strain sensor, on thekickback frame 5202 can be used to detect a kickback condition, withouthaving to use a pivot.

FIG. 54 illustrates one embodiment of the saw 10 having torque-basedkick back detection mechanism. When a kickback event occurs, theworkpiece may come into contact with a trailing or rear portion of theblade 14. This may increase the torque that the motor 40 must produce tomaintain a constant rotation of the blade 14. Accordingly, in suchembodiments, the saw 10 comprises one or more torque sensors 5402mounted on a shaft between the motor 40 and the blade 14. For example,the torque sensor 5402 may be mounted on the arbor shaft to which theblade 14 is secured, or some other drive shaft between the motor 40 andthe blade 14. The detection system 30 may be in communication with thetorque sensor(s) 5402. If the torque sensor(s) 5402 indicates that thetorque on the shaft has increased by more than a predetermined amount,it may indicate that a kickback condition has occurred. Accordingly, thedetection system 30 may trigger the mitigating reaction of the reactionsystem 32. Any suitable torque sensor 5402 may be used, such as straingauge torque sensors or surface acoustic wave (SAW) torque sensors.

According to various embodiments, embodiments of the present inventionare directed to a table saw that comprises: a cutting surface; amotor-driven, rotatable blade for cutting a workpiece on the cuttingsurface, wherein a portion of the blade is extendable above the cuttingsurface; a kickback detection system for detecting kickback of theworkpiece during cutting of the workpiece; and reaction means incommunication with the kickback detection system for taking a mitigatingreaction in response to detection of kickback of the workpiece duringcutting of the workpiece. According to various implementations, thekickback detection system comprises: an acoustic sensor; and a processorin communication with the acoustic sensor, wherein the processor isprogrammed to recognize a condition indicative of kickback of theworkpiece during cutting of the workpiece based on input from theacoustic sensor. The processor may be further programmed to determinewhether the blade is rotating based on input from the acoustic sensor,and, when it is determined that the blade is rotating, maintain thereaction means in an armed state. In addition, the kickback detectionsystem may comprise: a torque sensor mounted on the rotatable bladeshaft; and a processor in communication with the torque sensor, whereinthe processor is programmed to recognize a condition indicative ofkickback of the workpiece during cutting of the workpiece based on inputfrom the torque sensor. In other embodiments, the table saw furthercomprises: a motor positioned below the cutting surface; a rotatableblade shaft positioned below the cutting surface on which the blade ismounted; a clutch coupled to the blade shaft, such that when the clutchis engaged and the motor is running, the blade shaft is rotated; a brakesystem for braking the blade; and a motor shut-down circuit connected tothe clutch and the brake system, wherein the motor shut-down circuitdisengages the clutch and actuates the brake system to brake the bladewhen the motor is turned off.

According to other embodiments, the table saw comprises: a cuttingsurface; a motor-driven, rotatable blade for cutting a workpiece on thecutting surface, wherein a portion of the blade is extendable above thecutting surface; detection means for detecting a dangerous conditionrelative to the blade; reaction means in communication with thedetection means for taking a reaction in response to detection of thedangerous condition; and a blade-spin detection system for detectingwhether the blade is rotating based on energy from the blade, whereinthe blade-spin detection system is in communication with the reactionmeans and provides an output to arm the reaction means when theblade-spin detection system detects that the blade is spinning. Invarious implementations, the blade-spin detection system comprises astatic electricity charge sensor in proximity to the blade for sensingthe static electricity build-up on the blade. In other implementations,the blade-spin detection system comprises: a transmitter proximate tothe blade for transmitting radio signals; a passive electronic circuiton the blade that transmits responsive radio signals when passivelyenergized by the radio signals transmitted by the transmitter; and areceiver, proximate to the blade, for detecting the responsive radiosignals from the passive electronic circuit. In yet otherimplementations, the blade-spin detection system comprises: an acousticsensor; and a processor in communication with the acoustic sensor,wherein the processor is programmed to determine whether the blade isrotating based on input from the acoustic sensor. In yet otherimplementations, the blade-spin detection system comprises: an airflowsensor that senses airflow generated by the plurality of off-centerholes of the blade when the blade spins; and a processor incommunication with the airflow sensor, wherein the processor isprogrammed to determine whether the blade is rotating based on inputfrom the acoustic sensor. In yet other implementations, the blade-spindetection system comprises: one or more magnets mounted on the blade;and an inductor proximate to the blade, wherein the magnets, whenspinning with the blade, induce a voltage across the inductor, whereinthe reaction means is connected to the inductor. In addition, the tablesaw may further comprise a power converter having an input connected tothe inductor for converting the voltage across the inductor to an outputvoltage used to power the reaction means and/or the detection means.

According to various implementations, the blade comprises a plurality ofoff-center holes that extend through the blade. In addition, the tablesaw may further comprise an electrical generator connected by one ormore gears to the rotatable blade shaft, wherein the electricalgenerator is further connected to the reaction means and generateselectricity when the shaft rotates to power the reaction means and/orthe detection means. In addition, the reaction means may comprise: aclutch coupled to the blade shaft, such that when the clutch is engagedand the motor is running, the blade shaft is rotated, and wherein theclutch is disengaged when the detection means detects the dangerouscondition; and a brake system for braking the blade when the detectionmeans detects the dangerous condition. Additionally, the blade maycomprise an outer peripheral portion that comprises a first material, aninner portion that comprises a second material that is different fromthe first material, wherein the first material is denser than the secondmaterial. In addition, the table saw may further comprise: a flywheelthat rotates in a direction that is the same as a direction of rotationfor the blade, wherein the flywheel is coupled to the rotatable shaft bya clutch, and wherein the reaction means disengages the clutch when thedangerous condition is detected. In addition, the table saw may furthercomprise kickback mitigation means downstream from the blade formitigating kickback of the workpiece and/or a suction feed assembly thatfeeds the workpiece to the blade for cutting.

According to other embodiments, the table saw comprises: a cuttingsurface; a motor-driven, rotatable blade that is partially extendableabove the cutting surface for cutting a workpiece positioned on thecutting surface; and a sensor connected to the cutting surface forsensing a characteristic of the workpiece during cutting of theworkpiece. In various implementations, the table saw further comprises ablade height adjustment mechanism for adjusting a height of the bladerelative to the cutting surface, the sensor comprises a height sensorfor sensing a height of the workpiece relative to the cutting surface,and the table saw further comprises a height adjustment circuit thatreceives an input signal from the height sensor indicative of the heightof the workpiece relative to the cutting surface and outputs a signal tothe blade height adjustment mechanism to adjust the height of the bladebased on the height of the workpiece sensed by the height sensor. Inother implementations, the sensor comprises a workpiece conductivitysensor on the cutting surface that detects electrical conductivity ofthe workpiece. In such an implementation, the table saw may furthercomprise: contact detection means for detecting contact with the bladeby an object other than the workpiece, wherein the contact detectionmeans receives an input from the workpiece conductivity sensor anddetects contact with the blade by the object based on the input from theworkpiece conductivity sensor; and reaction means in communication withthe contact detection system for taking a mitigating reaction inresponse to detection of contact with the blade by the object. Theworkpiece conductivity sensor may comprise a wheel positioned adjacentto a trailing and/or leading edge of the blade, wherein the wheelcomprises one or more probes that extend into the workpiece to sense theelectrical conductivity of a portion of the workpiece after cutting ofthe portion by the blade.

According to other embodiments, the table saw comprises: a cuttingsurface; a motor-driven, rotatable blade for cutting a workpiece on thecutting surface, wherein a portion of the blade is extendable above thecutting surface; a contact detection system for detecting contact withthe blade by an object other than the workpiece; and reaction means incommunication with the contact detection system for taking a mitigatingreaction in response to detection of contact with the blade by theobject. The blade comprises: a first electrically conductive bladeportion; a second electrically conductive blade portion; and adielectric between the first and second electrically conductive bladeportions. The contact detection system is connected to the firstelectrically conductive blade portion and drives the first electricallyconductive blade portion with a drive signal, and wherein the contactdetection system comprises a processor for detecting contact with theblade by the object based on an electrical signal from the firstelectrically conductive blade portion. For example, the contactdetection system may detect contact with the blade by a foreign objectbased on the current drawn by the first electrically conductive bladeportion.

According to other embodiments, the table saw comprises: a cuttingsurface; a motor-driven rotatable shaft positioned below the cuttingsurface; a blade for cutting a workpiece on the cutting surface, whereinthe blade is mounted on the shaft, and wherein a portion of the blade isextendable above the cutting surface; a detection system for detecting adangerous condition relative to the blade; a reaction system incommunication with the detection system for taking a reaction inresponse to detection of the dangerous condition, wherein the reactionsystem comprises a magnetorheological rotary brake connected to theshaft that brakes the shaft to thereby brake the blade in response todetection of the dangerous condition by the detection system. In variousimplementations, the magnetorheological rotary brake comprises: a rotorfixed to the shaft; a housing, wherein the housing and the rotor definea spacing; magnetorheological fluid in the spacing; and a magneticfield-producing coil that is energized in response to detection of thedangerous condition by the detection system to produce a magnetic fieldthat causes the magnetorheological fluid to increase its viscosity tobrake the rotor, thereby braking the shaft, thereby braking the blade.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions, and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

What is claimed is:
 1. A table saw comprising: a cutting surface; amotor-driven, rotatable blade for cutting a workpiece on the cuttingsurface, wherein a portion of the blade is extendable above the cuttingsurface; detection means for detecting a dangerous condition relative tothe blade; reaction means in communication with the detection means fortaking a reaction in response to detection of the dangerous condition bythe detection system; and a blade-spin detection system, different fromthe detection means and the reaction means, for detecting whether theblade is rotating based on energy from the blade, wherein the blade-spindetection system is in communication with the reaction means andprovides an output to arm the reaction means when the blade-spindetection system detects that the blade is spinning so that the reactionmeans is armed to take the response when triggered by the detectionmeans.
 2. The table saw of claim 1, further comprising a kickbackdetection system for detecting kickback of the workpiece during cuttingof the workpiece; and wherein the reaction means is in communicationwith the kickback detection system and is further configured for takinga mitigating reaction in response to detection of kickback of theworkpiece by the kickback detection system during cutting of theworkpiece.
 3. The table saw of claim 2, wherein the kickback detectionsystem comprises: an acoustic sensor; and a processor in communicationwith the acoustic sensor, wherein the processor is programmed torecognize a condition indicative of kickback of the workpiece duringcutting of the workpiece based on input from the acoustic sensor.
 4. Thetable saw of claim 3, wherein the processor is further programmed todetermine whether the blade is rotating based on input from the acousticsensor, and, when it is determined that the blade is rotating, maintainthe reaction means in an armed state.
 5. The table saw of claim 2,wherein the kickback detection system comprises: a torque sensor mountedon a rotatable shaft used to rotate the blade; a processor incommunication with the torque sensor, wherein the processor isprogrammed to recognize a condition indicative of kickback of theworkpiece during cutting of the workpiece based on input from the torquesensor.
 6. The table saw of claim 2, further comprising: a motorpositioned below the cutting surface; a rotatable blade shaft positionedbelow the cutting surface on which the blade is mounted; a clutchcoupled to the blade shaft, such that when the clutch is engaged and themotor is running, the blade shaft is rotated; a brake system for brakingthe blade; and a motor shut-down circuit connected to the clutch and thebrake system, wherein the motor shut-down circuit disengages the clutchand actuates the brake system to brake the blade when the motor isturned off.
 7. The table saw of claim 1, wherein the blade-spindetection system comprises a static electricity charge sensor inproximity to the blade for sensing the static electricity build-up onthe blade.
 8. The table saw of claim 1, wherein the blade-spin detectionsystem comprises: a transmitter proximate to the blade for transmittingradio signals; a passive electronic circuit on the blade that transmitsresponsive radio signals when passively energized by the radio signalstransmitted by the transmitter; and a receiver, proximate to the blade,for detecting the responsive radio signals from the passive electroniccircuit.
 9. The table saw of claim 1, wherein the blade-spin detectionsystem comprises: an acoustic sensor; and a processor in communicationwith the acoustic sensor, wherein the processor is programmed todetermine whether the blade is rotating based on input from the acousticsensor.
 10. The table saw of claim 1, wherein the blade comprises aplurality of off-center holes that extend through the blade.
 11. Thetable saw of claim 10, wherein the blade-spin detection systemcomprises: an airflow sensor that senses airflow generated by theplurality of off-center holes of the blade when the blade spins; and aprocessor in communication with the airflow sensor, wherein theprocessor is programmed to determine whether the blade is rotating basedon input from the airflow sensor.
 12. The table saw of claim 1, whereinthe blade-spin detection system comprises: one or more magnets mountedon the blade; and an inductor proximate to the blade, wherein the one ormore magnets, when spinning with the blade, induce a voltage across theinductor, wherein the reaction means is connected to the inductor. 13.The table saw of claim 12, further comprising a power converter havingan input connected to the inductor for converting the voltage across theinductor to an output voltage used to power the reaction means.
 14. Thetable saw of claim 12, further comprising a power converter having aninput connected to the inductor for converting the voltage across theinductor to an output voltage used to power the detection means.
 15. Thetable saw of claim 1, wherein the blade is mounted on a rotatable shaft;and further comprising an electrical generator connected by one or moregears to the rotatable shaft, wherein the electrical generator isfurther connected to the reaction means and generates electricity whenthe shaft rotates to power the reaction means.
 16. The table saw ofclaim 1, wherein the blade is mounted on a rotatable shaft; and furthercomprising an electrical generator connected by one or more gears to therotatable shaft, wherein the electrical generator is further connectedto the detection means and generates electricity when the shaft rotatesto power the detection means.
 17. The table saw of claim 1, furthercomprising: a motor; and a motor-driven blade shaft on which the bladeis mounted; and wherein the reaction means comprises: a clutch coupledto the blade shaft, such that when the clutch is engaged and the motoris running, the blade shaft is rotated, and wherein the clutch isdisengaged when the detection means detects the dangerous condition; anda brake system for braking the blade when the detection means detectsthe dangerous condition.
 18. The table saw of claims 1, wherein theblade comprises: an outer peripheral portion that comprises a firstmaterial; and an inner portion that comprises a second material that isdifferent from the first material, wherein the first material is denserthan the second material.
 19. The table saw of claims 18, wherein: theblade is mounted on a rotatable shaft; the table saw further comprises aflywheel that rotates in a direction that is the same as a direction ofrotation for the blade, wherein the flywheel is coupled to the rotatableshaft by a clutch; and the reaction means disengages the clutch when thedangerous condition is detected.
 20. The table saw of claim 1, furthercomprising kickback mitigation means downstream from the blade formitigating kickback of the workpiece.
 21. The table saw of claim 1,further comprising a suction feed assembly that feeds the workpiece tothe blade for cutting.
 22. The table saw of claim 1, further comprisinga sensor connected to the cutting surface for sensing a characteristicof the workpiece during cutting of the workpiece.
 23. The table saw ofclaim 22, wherein: the table saw further comprises a blade heightadjustment mechanism for adjusting a height of the blade relative to thecutting surface; the sensor comprises a height sensor for sensing aheight of the workpiece relative to the cutting surface; and the tablesaw further comprises a height adjustment circuit that receives an inputsignal from the height sensor indicative of the height of the workpiecerelative to the cutting surface and outputs a signal to the blade heightadjustment mechanism to adjust the height of the blade based on theheight of the workpiece sensed by the height sensor.
 24. The table sawof claim 22, wherein: the sensor comprises a workpiece conductivitysensor on the cutting surface that detects electrical conductivity ofthe workpiece; and the detection means is for detecting contact with theblade by an object other than the workpiece, wherein the detection meansreceives an input from the workpiece conductivity sensor and detectscontact with the blade by the object based on the input from theworkpiece conductivity sensor; and the reaction means is for taking amitigating reaction in response to detection of contact with the bladeby the object.
 25. The table saw of claim 24, wherein the workpiececonductivity sensor comprises a wheel positioned adjacent to a trailingedge of the blade, wherein the wheel comprises one or more probes thatextend into the workpiece to sense the electrical conductivity of aportion of the workpiece after cutting of the portion by the blade. 26.The table saw of claim 24, wherein the workpiece conductivity sensorcomprises a wheel positioned adjacent to a leading edge of the blade,wherein the wheel comprises one or more probes that extend into theworkpiece to sense the electrical conductivity a portion of theworkpiece prior to cutting of the portion by the blade.
 27. The tablesaw of claim 1, wherein: the detection means is for detecting contactwith the blade by an object other than the workpiece; and the bladecomprises: a first electrically conductive blade portion; a secondelectrically conductive blade portion; and a dielectric between thefirst and second electrically conductive blade portions, and thedetection means is connected to the first electrically conductive bladeportion and drives the first electrically conductive blade portion witha drive signal, and wherein the detection means comprises a processorfor detecting contact with the blade by the object based on anelectrical signal from the first electrically conductive blade portion.28. The table saw of claim 27, wherein the second electricallyconductive blade portion comprises teeth for cutting the workpiece. 29.The table saw of claim 1, further comprising a motor-driven rotatableshaft positioned below the cutting surface, wherein the blade is mountedon the shaft, and wherein the reaction means comprises amagnetorheological rotary brake connected to the shaft that brakes theshaft to thereby brake the blade in response to detection of thedangerous condition by the detection system.
 30. The table saw of claim29, wherein the magnetorheological rotary brake comprises: a rotor fixedto the shaft; a housing, wherein the housing and the rotor define aspacing; magnetorheological fluid in the spacing; and a magneticfield-producing coil that is energized in response to detection of thedangerous condition by the detection system to produce a magnetic fieldthat causes the magnetorheological fluid to increase its viscosity tobrake the rotor, thereby braking the shaft, thereby braking the blade.